Once again this morning, we're learning of the many ways that a changing climate can change our lives. Yesterday, our series Climate Connections with National Geographic took us to South America, where the destruction of rainforest can spread malaria. Yellow fever is also spreading in parts of South America.

The cause is not clear, but some scientists warn that global warming could lead to a spread of disease as mosquitoes and other carriers expand where they can live. If you think that kind of threat is far off for the United States with its better sanitation and other health systems, note that Americans, too, were once terrorized by yellow fever. In the 17 and 1800s, Philadelphia, New York and New Orleans all experienced outbreaks. The worst swept through Memphis, Tennessee like a biblical plague. NPR's Joseph Shapiro tells the story.

JOSEPH SHAPIRO: People in Memphis reported strange weather in 1878. It was hot that year, and it got hot early.

Ms. MOLLY CALDWELL CROSBY (Author): There were newspaper articles and personal accounts that the flowers had bloomed in January and February. By March, we're already having 80 degree temperatures.

SHAPIRO: That's Molly Caldwell Crosby. She's written "The American Plague." It's a history of yellow fever.

Ms. CROSBY: It's a very ugly disease, with things like eyes bleeding, nose, ears, some pretty gruesome symptoms. But then it also causes internal bleeding. And one of the tell-tale signs of yellow fever is what they call black vomit. It's from digesting internal bleeding.

SHAPIRO: A victim's skin and the whites of their eyes turn yellow.

Ms. CROSBY: One New Orleans doctor performing an autopsy that summer described it as bright canary yellow.

SHAPIRO: There had been yellow fever epidemics in Memphis before, but never anything like the outbreak in 1878. Back then, Memphis was a busy trade route for the steamboats that went up and down the Mississippi river. Crosby brings me to a neighborhood of old brick buildings close to the water.

Ms. CROSBY: And this would have been ground zero for the outbreak of yellow fever. It was right along the shore of the Mississippi river. There was a lot of poverty, they did have sanitation problems.

SHAPIRO: The Memphis board of health officially reported the first case on August 14th, 1878. That woman ran a snack shop in this neighborhood. News of her death set off mass panic.

Mr. CROSBY: And within hours, the woman's body was burned, her building was closed off, and in the next three days, they had between 20 and 25,000 people leave the city.

SHAPIRO: More than half the city's population fled. People left front doors wide open and their silverware set on the dinning room table. Those who stayed behind were largely poor. Many were immigrants, many were black. Of 19,000 people who stayed, 17,000 got sick. More than 5,000 would die.

(Soundbite of music, "Jesu, Joy of Man's Desiring")

SHAPIRO: One who did stay behind was Sister Constance here at St. Mary's Episcopal Cathedral. She went from house to house to care for the sick. Sometimes she found abandoned children amidst the rotting corpses of their parents. People thought the disease was spread by bad air, so even though temperatures were close to 100 degrees that summer, they boarded up their windows and kept fires burning to ward off the outside air. And when someone died, their clothing and even their beds were dragged into the street and burned because it was thought that would keep the disease from spreading. After just a few weeks, Sister Constance started to shake, and her own skin turned hot to the touch. She knew what that meant. Author Molly Crosby writes that when the other sisters made up their best mattress with fresh linens, Sister Constance said no and took a cot instead.

Ms. CROSBY: She was sick for several days. The night before she died, she said to her nurse, I shall never get up from my bed. And it was - her last words were Alleluia Hosanna, Praise be to God.

SHAPIRO: Today, those words are engraved in the altar at St. Mary's along with the names of the six nuns and priests who died caring for the sick. They're now celebrated as martyred saints by the Episcopal Church.

Ms. ELIZABETH WIRLS: You really do feel their presence.

SHAPIRO: Elizabeth Wirls works here at St. Mary's.

Ms. WIRLS: It's like they're calling to you. You can do more. It's about -we're being called to do for others, no picking and choosing who you do it for.

(Soundbite of bell ringing)

SHAPIRO: The nuns and priests are buried here at Elmwood Cemetery.

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SHAPIRO: Every time a yellow fever victim was buried, the cemetery keeper's young daughter, Grace, would ring this bell - until she came down sick, too. The worse of the epidemic lasted for six weeks. Molly Crosby writes that often, the only people who dared go out on the streets were the collectors of the bodies. With horse and wagon, they shouted bring out your dead. They took the bodies to this cemetery for a hasty burial.

Ms. CROSBY: We are standing over 1,400 bodies right here. This was a large mass grave. The gravediggers were burying over 50 people a day, and sometimes only six inches beneath the soil. They didn't have time to dig a full six feet. They believed at that time that the corpses could also be spreading disease, so they were trying to get them under the ground as quickly as possible.

SHAPIRO: The names of the dead were written in ink in leatherbound ledgers. Kim Caldwell, Elmwood's director, reads.

SHAPIRO: People waited anxiously for fall and the first frost. From experience, they knew that's when the deaths would stop.

Ms. CALDWELL: Colonel A.S. Brown, yellow fever, no age.

SHAPIRO: But in 1878, they had no idea why. It would be another two decades before it was widely understood that yellow fever was spread through the bite of a mosquito, and that the infected insect stowed away on shipments from Africa that went through the Caribbean and then on boats to New Orleans and up the Mississippi. Today, Memphis is still a transit hub for airplanes, trains, and just like in the 1800s, for boats. For our last stop, Crosby's brought me to a bluff above the wide Mississippi river.

Ms. CROSBY: We're looking over towards President's Island. That's where a lot of the ships came through, the John D. Porter, the Golden Crown, a number of the boats that came through that landed feverish people in Memphis.

SHAPIRO: Because of the warm weather in 1878, this city had two or three times as many mosquitoes as usual. They bit someone who was already infected, then bit somebody else, and the disease kept spreading. Today, yellow fever's no longer much of a threat in this country. There's a vaccine, modern sewer systems, and ways to control mosquitoes. But 25 years ago, a scientist working at another Memphis cemetery - just down the street from the one with all the graves of yellow fever victims - checked a trap and discovered the first Asian tiger mosquito found in the United States. That mosquito spreads another illness: West Nile virus.

Some scientists blame global warming for the tiger mosquito's spread to 26 states and as far north as Illinois. But those first mosquitoes got to the United States the same way as the ones that first brought yellow fever, by breeding in pools of water on boats that made their way across the ocean.

Joseph Shapiro, NPR News.

INSKEEP: You can hear more stories on climate change at npr.org/climateconnections, where you can also watch videos from around the world on climate science in action. That's from public television's Wild Chronicles.

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